Before installing 10.8 mailboxes were separated.

After installing Mountain Lion, the mailboxes in iMail are now all listed on the left hand side. Before the upgrade, most of these mailboxes (all of them created by me) were in a separate folder so that I didn't have to see them all the time. I have tried to figure out how to get them intio a folder again so I can reference them when I need to.

Thank you for your help.